1. Field of the Invention
This invention relates to a digital signal conversion apparatus and digital signal conversion method that performs Pulse Width Modulation (PWM) on an input digital signal and converts it to an analog signal.
2. Description of the Related Art
One typical well-known method used by digital-to-analog converters for converting an input digital signal to an analog signal is the so-called PWM method, which converts an input digital signal to a PWM waveform and then converts that to an analog signal. The PWM method is also used in digital amps (D-class amp) that drive loads such as speakers or the like based on the input signal. The PWM of a digital signal (hereafter referred to as simply digital PWM) inevitably generates non-linear distortion.
Conventionally, 2-value PWM in which the PWM waveform takes the two values +1 and −1, and 3-value PWM in which the waveform takes the three values +1, 0 and −1 have been known as PWM modulation methods. Since 3-value PWM generates no even-ordered non-linear distortion, it is preferred to 2-value PWM from the aspect of lower distortion rate.